Whitening cosmetics which contain a substance having a whitening effect as an active ingredient for preventing dermal pigmentation or formation of spots or freckles due to the sunburn have been proposed. For example, a whitening cosmetic containing a placenta extract or a vitamin C derivative as an active ingredient with or without a vegetable extract or an .alpha.-hydroxylic acid (lactic acid, glycolic acid, etc) as a moisturizing component for enhancing the expected efficacy of such an active ingredient has been proposed.
On the other hand, based on findings that tyrosinase is involved in a melanin biosynthesis mechanism which is associated with dermal pigmentation, a whitening skin care product containing, as an active ingredient, arbutin or kojic acid which has a tyrosinase activity inhibiting effect has also been proposed.
However, the biosynthesis of melanin is known to take place in a melanocyte present in the basal layer which is the deepest place in an epidermis. It is also known that a corneal layer which forms a surface of human skin has a physiological function as a barrier against the invasion of to foreign bodies from an extracorpreal region. Therefore, application to the skin of a simple mixture of a whitening component with a commonly used cosmetic formulation base allows only a trace amount to penetrate the corneal layer to reach the basal layer and makes it difficult for the efficacy of the whitening component to be exerted. Accordingly, various percutaneous absorption promoters have been proposed and employed in the fields of pharmaceuticals and cosmetics for the purpose of facilitating the absorption of an active ingredient via the skin.
Nevertheless, problems still exist which include the difficulty in selecting an optimum combination of a whitening component and a known percutaneous absorption promoter as well as the absence of satisfactory efficacy and safety which should be possessed by a dermal topical formulation. In addition, increasing the whitening component content in a formulation in an attempt to increase the whitening effect based on the fact that the whitening component can itself be slightly absorbed via the skin is not recommended since it is problematic in terms of safety and cost.